Conventionally, there has been known oxygenators configured to conduct gas exchange using a hollow fiber membrane layer with multiple integrated hollow fiber membranes, as shown, for example, in JP4366268. The oxygenator disclosed in JP4366268 has a housing, an entirely circular cylindrical hollow fiber membrane layer stored in the housing, a blood inlet, a blood outlet, a gas inlet, and a gas outlet, wherein gas exchange, that is, oxygenation and decarbonation, takes place between blood and gas via the hollow fiber membranes.
There is a demand for oxygenators in which the filling amount of blood is decreased to reduce the amount of blood circulating extracorporeally.
In conventional oxygenators, however, the filling amount of blood cannot be reduced without lowering gas exchange performance and increasing a pressure loss during flowing of the blood.
It would be advantageous to provide an oxygenator with favorable gas exchange performance that creates a relatively small pressure loss during flowing of blood and needs only a small filling amount of blood.